1. Field of the Invention
This invention relates to apparatus and methods for testing for the presence of antigens using antibodies.
2. Prior Art
Valkirs et al disclose in U.S. Pat. No. 4,727,019 a device having a body member that contains a porous mass. A membrane having a ligand-receptor is disposed above the porous mass. The sample solution flows into the porous mass by capillary action only. There is no teaching of any means to reduce pressure to facilitate more rapid liquid transfer.
In U.S. Pat. No. 4,090,850 issued to Chan, an antibody coated cellulose paper is used in radioimmunoassays in conjunction with the test apparatus comprising a receptacle tray with multiple wells. Each of said wells having at its bottom an orifice such that the multiple wells can be simultaneously evacuated by a single source of reduced pressure.
In U.S. Pat. No. 3,888,629 issued to Bagshawe, a reaction cell for the performance of radioimmunoassay determinations and the like is disclosed. Here two halves of the cell are joined together, separated by a membrane containing the necessary antibodies to form a particulate reaction product. The liquid reagents flow through the membrane under the influence of gravity.
U.S. Pat. No. 4,424,279 issued to Bohn discloses an immunoassay apparatus having a cylindrical tube that has a plunger filter assembly slideably fitted therein. The filter is dome shaped and contains beads sensitized with immunologically reactive material.
Greenspan U.S. Pat. No. 4,189,385 discloses a method and apparatus for separating serum or plasma from the formed elements of blood. The apparatus disclosed is generally similar to that of Bohn, except instead of a filter, a one way valve is disclosed.
In Buono U.S. Pat. No. 4,057,499, another apparatus for the separation of blood is taught. The apparatus is similar to the apparatus disclosed in Bohn and Greenspan. The one way valve of Greenspan is a filter, but unlike the filter in Bohn, it contains no immunologically reactive material.
Moore et al. U.S. Pat. No. 3,870,639 teaches yet another similar blood plasma separation device. Other filtration devices include U.S. Pat. No. 4,522,713 to Nussbaumer and U.S. Pat. No. 3,687,246 to Spinosa.
Bohn, Greenspan, and Buono rely on a slight pressure differential being created when a plunger portion is forced into contact with fluid contained in an outer tube. The fluid beneath the plunger filter or valve is then forced upwardly into a receiver tube fitted within the outer tube.
A problem with prior testing devices is that an analytical laboratory, complete with vacuum lines is required to use the devices. It would be advantageous to have a device that requires no external source of vacuum. The present invention provides an externally manipulable piston for creating a region of reduced air pressure beneath a membrane binding an analytic compound, preferably an antibody. The region of reduced pressure causes the fluid to be tested to be rapidly drawn through the membrane.
Another problem with prior art devices has been that much of the sample never contacts the receptor site. Tests with increased sensitivity would result if all the sample contacted the receptor region.
Our popular structure for immunotesting devices is an immunoactive substrate bound to a membrane which lies upon an absorbent body. These embodiments do not feature an air gap. Typical prior art devices using this approach are shown in U.S. Pat. No. 4,632,901 and 4,727,019 both issued to Valkirs and U.S. Pat. No. 4,366,241 issued to Tom.
If a biological sample provides large enough amounts of analyte and the analyte and the immunoactive substrate react rapidly enough, then such devices are satisfactory. However, many times the analyte is found only in minute quantities or the analyte and the immunoactive substrate react slowly.
In cases like this it would be advantageous to have a different configuration of the immunotesting device. Such a configuration would allow sufficient time for the analyte and the immunoactive substrate to react.